These studies will investigate the effects of food deprivation on self- administration of commonly-used and abused drugs, and the subjective and physiological effects of these drugs in normal volunteers. The three drugs to be studied are marijuana, alcohol, and tobacco. The subjective and physiological effects of these drugs will be assessed concurrently with changes in drug intake, under conditions in which subjects have and have not restricted their food intake. In two of the studies, subjects in a fed or fasting (24 hour) state will sample marijuana and alcohol (and placebo) and then later choose whether they want to self-administer more of the substance. Subjective and physiological effect will be measured during the sampling period. In the third study, the effects of acute (24 hours) food deprivation on smoking behavior, smoke exposure, and mood states will be examined. In the fourth study, smoking behavior will be examined in overweight smokers enrolled in a 10 week weight-loss program. All four studies will explore whether food deprivation increases drug intake in humans, as it does in laboratory animals. Further, underlying mechanisms for increased drug intake may be examined via the measurement of other drug actions, i.e., their subjective and physiological effects.